On the last episode Jack asked Locke (MIB) if he was impersonating Jack's father Christian Shephard on their third day on the island. After Locke answers yes, as the discussion continues and from the previous episodes we understand tha after real Locke's death, MIB is stuck on John's body. However, if we rewatch the 9th episode of the 5th Season (Namaste), we see Cristian Shephard talking to Frank and Sun and showing them a photo of the new recruits back on 1977. Before we see Cristian we hear the whispers, but here stands a big questionmark. Locke was already dead and MIB was stuck on his body. So, who was he?? As we see, dead people can only Hurley see and not the other Losties, so we can assume that he is not a dead spirit trapped on the island as Michael told to Hugo. Who was Cristian?? Can Jacob or anybody else impersonate dead people?
Thank you for reading. I am open to other opinions and feel free to say what you think.